In recent years medical devices have gained significant acceptance in the medical community as an important treatment modality for heart diseases and other serious ailments, which were traditionally remedied by medication or surgical operation. Two fundamental trends have emerged in the treatment of cardiac diseases. The first has been the shift from open-heart surgical procedures to less invasive and less expensive catheter-based treatments, which are safer and less debilitating.
The second trend is represented by the shift from the use of anti-arrhythmic drugs to minimally invasive catheters or other device-based therapies to palliate incurable arrhythmias. For example, automatic cardioverter-defibrillator are routinely implanted in patients with lethal ventricular arrhythmias to reduce the likelihood of sudden death. Thus, radio-frequency (RF”) catheter ablation is now being performed in large number of patients suffering from cardiac arrhythmias.
Despite these advances in technology, atrial fibrillation (“AF”) remains a significant challenge. AF, a rapid irregular rhythm in the atria or upper chambers of the heart induced by non-uniformed electrical pulses, represents a leading cause of stroke and heart attack and a major health care burden. To date, the most effective surgical procedure for the treatment of AF has been the Maze procedure undertaken in “open-heart” surgery. In the Maze procedure, incisions are made along pre-determined lines exterior of the atrium, which are then sutured together. As healing develops, scars are formed along the incision lines thereby forming barriers to the conduction of electrical impulses. By creating such barriers, AF can no longer be sustained and regular heart rhythm is restored. However, the Maze procedure has not been widely adopted due to the cost and mortality associated with open-heart surgery, but only as adjunct to other major procedures such as mitral-valve replacement.
One new approach to mimic the Maze operation is represented by catheter-based radio-frequency ablation technique, wherein, instead of surgical incisions, a catheter-antenna is applied to destroy or ablate the heart tissues inside the atrial chamber. The catheter-antenna is passed through the vein for access to the atrium, as commonly practiced in the medical field. Within the atrium, the tip of the catheter-antenna is positioned, usually with the aid of x-ray or fluoroscopic means, and is brought into contact with the heart tissue at a desired location or spot where ablation is required. At this spot, the tissue is destroyed by resistive heating generated from the catheter-antenna. Thereafter, the catheter-antenna is re-positioned to the next spot for ablation. A series of spot ablations thus mimics the linear lesions as accomplished under the Maze procedure against the conduction of electrical impulses.
Existing catheter-based ablation procedures are recognizably less intrusive than “open-heart” surgery. In addition, during the ablation, disruption of cardiovascular function is reduced. However, a successful catheter-based radio-frequency ablation procedure requires the ablation of tissue spots within the spatial or proximity tolerance between adjacent spots, usually less than 2 millimeters, to prevent the passage of electrical impulses. In that connection, the task for the precise placement of the catheter-antenna represents a critical element of a successful procedure.
A major drawback of such existing procedures is in the time-consuming task in positioning the catheter-antenna at the desired ablation spots within the atrium while the heart chamber muscles are pulsating. Movements of atrial wall or the heart muscles often render accurate placement of the catheter-antenna difficult, and slippage of the catheter-antenna tends to occur thereby damaging portions of the atrium where ablation is not desired. As a result, placement of the catheter based RF ablation cannot be efficiently accomplished, and prolonged procedure time, in excess of 12 hours, can be expected. Further, during the procedure, x-ray or other irradiating means are routinely employed for locating and positioning the catheter-antenna, which dictates the use of heavy lead protective gear by the electro-physiologist. As a result, such inconvenience is often amplified by the prolonged procedure time, which detracts from the use of catheter-based antenna as an efficient means for tissue ablation.
To minimize the risk of slippage, for example, in U.S. Pat. No. 5,741,249, a catheter-based microwave antenna is disclosed wherein a distal tip is incorporated into the antenna to anchor it to the atrial wall. However, while this design reduces the likelihood of antenna or catheter-antenna slippage during each ablation step, it does not eliminate the consuming task to secure precise placement of the antenna along the desired ablation path for each ablation step. Thus, after each ablation step, the antenna has to be re-positioned and anchored precisely at the next spot which must be located within the spatial or proximity tolerance on the ablation path as referenced above.
Accordingly, effective treatments for atrial fibrillation with catheter ablation will require the creation of long or overlapping linear or curvilinear ablation lesions on the inner surface of the atrium. These lesions can then act as barriers to the conduction of electrical impulses, thus preventing atrial fibrillation.
A critical requirement for the effective catheter-based ablation of atrial fibrillation is the ability to stabilize and anchor the catheter and microwave antenna inside the atrial chambers. New catheter ablation systems capable of stabilizing and anchoring the catheter and microwave antenna inside the atrial chambers, preferably capable of producing long or overlapping linear or curvilinear ablation lesions, are required for the development of minimally invasive catheter-based curative procedures for atrial fibrillation.
U.S. Pat. No. 6,190,382, issued Feb. 20, 2001 and U.S. patent application Ser. No. 09/459,058, filed Dec. 11, 2000, which are incorporated by reference as though set forth in full and include the same inventors as the present application, disclose a radio-frequency or microwave-energy based catheter for ablating biological tissues within the body vessel of a patient. The catheter has a proximal portion, a distal portion with a distal end and a lumen extending from the proximal portion to the distal portion. The catheter incorporates an elongated catheter guide that is located within the catheter lumen and is secured to the distal portion of the catheter at one end, with the other end portion extending proximally within the catheter lumen to be coupled to a positioning mechanism. A significant advantage of the catheter guide is that it is deployable beyond the distal end of the catheter to form a loop, which is conformable to the interior contour of the body vessel. The catheter guide carries the catheter with a radio-frequency or microwave energy based antenna incorporated at the distal portion of the catheter. The antenna includes a helical coil, which accommodates the catheter guide passing through it.
The radio-frequency antenna is adapted to receive and irradiate radio-frequency energy in the microwave range at a frequency typically greater than 300 Megahertz (MHz) in the electromagnetic spectrum for ablating biological tissue along a biological ablation pathway.